using TestDbContext ctx = new TestDbContext(); var b1 = new Book { AuthorName = "杨中科", Title = "零基础趣学C语言", Price = 59.8, PubTime = new DateTime() }; var b2 = new Book { AuthorName = "Robert Sedgewick", Title = "算法(第4版)", Price = 99, PubTime = new DateTime() }; var b3 = new Book { AuthorName = "吴军", Title = "数学之美", Price = 69, PubTime = new DateTime() }; var b4 = new Book { AuthorName = "杨中科", Title = "程序员的SQL金典", Price = 52, PubTime = new DateTime() }; var b5 = new Book { AuthorName = "吴军", Title = "文明之光", Price = 246, PubTime = new DateTime() }; ctx.Books.Add(b1); ctx.Books.Add(b2); ctx.Books.Add(b3); ctx.Books.Add(b4); ctx.Books.Add(b5); await ctx.SaveChangesAsync(); Console.WriteLine("-==============测试=============="); Console.WriteLine(long.MaxValue);
查询数据库
using TestDbContext ctx = new TestDbContext(); foreach (Book b in ctx.Books) { Console.WriteLine($"Id={b.Id},Title={b.Title},Price={b.Price}"); } Console.WriteLine("-==============测试=============="); Console.WriteLine(long.MaxValue);
条件查询
Console.WriteLine("***所有价格高于80元的书籍***"); IEnumerable<Book> books2 = ctx.Books.Where(b => b.Price > 80); foreach (Book b in books2) { Console.WriteLine($"Id={b.Id},Title={b.Title},Price={b.Price}"); }
//数据的插入 /* using TestDbContext ctx = new TestDbContext(); var b1 = new Book{ AuthorName = "杨中科", Title = "零基础趣学C语言", Price = 59.8, PubTime = new DateTime(2019, 3, 1) }; var b2 = new Book{ AuthorName = "Robert Sedgewick", Title = "算法(第4版)", Price = 99, PubTime = new DateTime(2012, 10, 1) }; var b3 = new Book{ AuthorName = "吴军", Title = "数学之美", Price = 69, PubTime = new DateTime(2020, 5, 1) }; var b4 = new Book{ AuthorName = "杨中科", Title = "程序员的SQL金典", Price = 52, PubTime = new DateTime(2008, 9, 1) }; var b5 = new Book{ AuthorName = "吴军", Title = "文明之光", Price = 246, PubTime = new DateTime(2017, 3, 1) }; ctx.Books.Add(b1); ctx.Books.Add(b2); ctx.Books.Add(b3); ctx.Books.Add(b4); ctx.Books.Add(b5); await ctx.SaveChangesAsync();*/ //查询 /* using TestDbContext ctx = new TestDbContext(); Console.WriteLine("***所有书籍***"); foreach (Book b in ctx.Books) { Console.WriteLine($"Id={b.Id},Title={b.Title},Price={b.Price}"); } Console.WriteLine("***所有价格高于80元的书籍***"); IEnumerable<Book> books2 = ctx.Books.Where(b => b.Price > 80); foreach (Book b in books2) { Console.WriteLine($"Id={b.Id},Title={b.Title},Price={b.Price}"); }*/ //Single、FirstOrDefault查询 /* using TestDbContext ctx = new TestDbContext(); Book b1 = ctx.Books.Single(b => b.Title == "零基础趣学C语言"); Console.WriteLine($"Id={b1.Id},Title={b1.Title},Price={b1.Price}"); Book? b2 = ctx.Books.FirstOrDefault(b => b.Id == 9); if (b2 == null) { Console.WriteLine("没有Id=9的数据"); } else { Console.WriteLine($"Id={b2.Id},Title={b2.Title},Price={b2.Price}"); }*/ //排序 /* using TestDbContext ctx = new TestDbContext(); IEnumerable<Book> books = ctx.Books.OrderByDescending(b => b.Price); foreach (Book b in books) { Console.WriteLine($"Id={b.Id},Title={b.Title},Price={b.Price}"); }*/ //GroupBy using TestDbContext ctx = new TestDbContext(); var groups = ctx.Books.GroupBy(b => b.AuthorName) .Select(g => new { AuthorName = g.Key, BooksCount = g.Count(), MaxPrice = g.Max(b => b.Price) }); foreach (var g in groups) { Console.WriteLine($"作者:{g.AuthorName},图书数量:{g.BooksCount},最高价格:{g.MaxPrice}"); } //修改数据 /* using TestDbContext ctx = new TestDbContext(); var b = ctx.Books.Single(b => b.Title == "数学之美"); b.AuthorName = "Jun Wu"; await ctx.SaveChangesAsync(); */ //删除数据 /* using TestDbContext ctx = new TestDbContext(); var b = ctx.Books.Single(b => b.Title == "数学之美"); ctx.Remove(b);//也可以写成ctx.Books.Remove(b); await ctx.SaveChangesAsync();*/ /* using TestDbContext ctx = new TestDbContext(); Book b = new Book { AuthorName = "Zack Yang", Title = "Zack, Cool guy!", Price = 9.9, PubTime = new DateTime(2020, 12, 30) }; ctx.Books.Add(b); Console.WriteLine($"保存前,Id={b.Id}"); await ctx.SaveChangesAsync(); Console.WriteLine($"保存后,Id={b.Id}");*/
标签:TestDbContext,Title,C#,ctx,Price,改查,efcode,Books,new From: https://www.cnblogs.com/zhulongxu/p/17739181.html